The basic operation of an electrostatographic printing machine is well known to those of ordinary skill. The term "electrostatographic" encompasses both electrophotographic and electrostatic printing. Typically, electrophotographic and electrostatic printing methods utilize a developer roll and a developer roll sleeve in the manner described below, except that electrostatic printing uses an insulating medium while electrophotographic printing uses a photosensitive medium to record an electrostatic latent charge image pattern on the medium.
Inasmuch as the art of electrophotographic printing is well known, reference is made to FIG. 1 which schematically depicts various parts of an exemplary electrophotographic printing machine. As depicted in FIG. 1, a drum 10 having a photoconductive surface 12 is positioned to rotate in direction 14 about a central axis 15. Around the periphery of drum 10 are provided a first corona generating device 16, an exposure station 18, a developer station 20, a substrate stack 22 to supply single sheets of substrate 22a (via registration rolls 30, 31, and 32 rotating in the direction indicated by arrows 34 to advance single sheets of substrate 22a through chute 31a), a second corona generating device 36, an endless belt 38, a fixing station 60, and a cleaning mechanism 40. These components are used in concert to produce a duplicate image of an original image (not shown) onto a substrate surface such as paper. The various steps involved in a "printing cycle" are described in greater detail below.
During a typical electrophotographic printing cycle, the drum 10 is routinely rotated (typically at uniform speed) in direction 14 to interact with the various components of an electrophotographic printing machine. A typical printing cycle begins with the exposure of the photoconductive surface 12 to a uniform electrostatic charge at the first corona generating station 16 as drum 10 is rotated in direction 14 thereunder. Thus, under the influence of the first corona generating device 16, the photoconductive surface 12 becomes uniformly charged. As it is subsequently rotated under exposure station 18, the uniformly charged photoconductive surface 12 is exposed to a photographic light image (of an original image to be duplicated). During such exposure, photoconductive surface 12 on drum 10 is rotated about axis 15 (typically at a uniform rate). Thereby, a duplicate image of the original image intended to be copied is recorded on the photoconductive surface 12 in the form of an electrostatic latent charge image pattern.
At exposure station 18, exposing light causes the uniform charge on surface 12 of drum 10 to be dissipated to yield the electrostatic latent charge image pattern as noted below. The amount of the uniform charge dissipated is proportional to the intensity of the exposing light. Those portions of photoconductive surface 12 not exposed to light at exposure station 18 continue to maintain a uniform charge. Thus, exposed portions of photoconductive surface 12 exhibit a dissipation of the uniform electrostatic charge while non-exposed portions maintain a uniform electrostatic charge. Thereby, photoconductive surface 12 now retains an electrostatic latent charge image pattern which corresponds to the photographic image of the original document. As photoconductive surface 12 on drum 10 is rotated beyond exposure station 18, the electrostatic latent charge image pattern recorded thereon is now ready for "development" at developer station 20.
Development of the electrostatic latent charge image recorded on the photoconductive surface 12 is achieved by transferring toner to the photoconductive surface 12. For proper development, the toner is transferred to the photoconductive surface 12 in a manner that duplicates the pattern of the electrostatic latent charge image. Effective development is accomplished by transferring toner particles to the electrostatic latent charge image at a controlled rate so that the toner particles adhere electrostatically to the charged areas of the recorded electrostatic latent image. Typically, the degree of transfer of the toner to photoconductive surface 12 at developer station 20 is proportional to the charge carried by the electrostatic latent image.
Commonly, either a one-component (a single component toner) or a two-component toner (carrier and toner) may be used for development of the electrostatic latent charge image. A typical two-component toner comprises toner particles tribo-electrically attached to magnetic carrier granules or beads. A typical one-component toner is a single component particle which has both magnetic and electrostatic properties. When the one-component or the two-component toner is placed in a magnetic field, the toner particles form what is known as a "magnetic brush." In particular, the toner particles within the magnetic field form relatively long chains which resemble the fibers of a brush. Thus, the term "magnetic brush" is aptly descriptive.
The developer roll 8 is optionally provided with a cylindrical sleeve 8a. Typically, the developer roll 8 is provided with an assembly of permanent magnets (not shown). Under the influence of a magnetic field (e.g., produced by the assembly of permanent magnets within the developer roll), the toner particles form the "magnetic brush" on the outer periphery of the developer roll 8 or on the outer periphery of the optimal developer roll sleeve 8a.
At the developer station 20, when the electrostatic latent charge image is advanced adjacent to the magnetic brush at nip 100b, the electrostatic charge on the photoconductive surface 12 is so biased that it attracts the toner particles away from the magnetic brush disposed on developer roll sleeve 8a (or on developer roll 8).
While a "magnetic brush" development scheme has been described, other development schemes such as "scavengeless" development, single component development, single component scavengeless development and the like may be used. Each of these development schemes use a developer roll sleeve, a developer roll or an equivalent thereof.
By the transfer of toner particles, the photoconductive surface 12 now carries on its surface toner particles in a pattern that corresponds to the electrostatic latent charge image, which in turn corresponds to the photographic image of the original document intended to be duplicated. Hereinafter, the photoconductive surface 12 having toner particles deposited thereon in the aforementioned manner is referred to as the "developed" toner image.
As the drum 10 (together with the developed toner image) is advanced beyond developer station 20, registration rolls 30, 31, and 32 are rotated in the direction of arrows 34 to advance single sheets of substrate 22a (e.g., paper) through chute 31a. In general, chute 31a directs the advancing sheet of substrate 22a into contact with drum 10 in a timed relationship so that the developed toner image contacts the advancing sheet of substrate 22a at nip location 100, situated between the second corona generating device 36 and drum 10. Preferably, the exemplary single sheet of substrate 22a is advanced to simultaneously arrive at nip 100 at about the same time as does the leading edge of the developed toner image disposed on surface 12 of drum 10. At least substantially simultaneously, the second corona generating device 36 is powered-up to apply a spray of ions onto the backside of substrate sheet 22a disposed adjacent to the developed toner image at nip location 100. Thereby, the single substrate sheet 22a is so charged as to cause transfer of the developed toner image (i.e., toner particles adhering to the photoconductive surface 12) directly onto the substrate sheet 22a. By such transfer, the toner is deposited onto substrate sheet 22a in a pattern which corresponds to the image of the original document intended to be duplicated.
Substrate sheet 22a is then advanced by endless belt 38 through fuser rolls/pressure rolls 69 and 70 to heat and permanently affix the transferred toner pattern onto substrate sheet 22a. Accordingly, the pattern corresponding to the original document intended to be copied is permanently affixed onto substrate sheet 22a. Appropriate rotation of fuser rolls/pressure rolls 69 and 70 advances the substrate sheet 22a onto collection tray 64.
Invariably, after transfer of the toner (from the developed toner image on photoconductive surface 12) onto substrate sheet 22a, some residual toner remains attached to photoconductive surface 12. To remove any residual toner, the photoconductive surface 12 is now advanced to cleaning mechanism 40. After cleaning, a discharge lamp (not shown) is used to flood the entire photoconductive surface 12 with light to dissipate any residual electrostatic latent charge that may be present thereon. In this manner, the photoconductive surface 12 is returned to its initial electrostatic charge level present immediately prior to uniform recharging thereof by the first corona generating device 16. The foregoing procedure outlines a typical "printing cycle" of an electrophotographic printing machine.
Repetition of the above-noted "printing cycle" procedure permits use of drum 10 in conjunction with developer roll 8 and/or developer roll sleeve 8a for another duplication cycle. The photoconductive surface 12, the developer roll 8, and the developer roll sleeve 8a are repeatedly used in the fashion indicated above. Such repeated use ultimately causes undesirable degradation of surface 9. Problems on surface 9 associated with degradation include, but are not limited to, undesirable streaking and ghosting. To reduce the wear and tear on the developer roll 8 and/or the developer roll sleeve 8a caused by their repeated use, it is desirable to provide a wear-resistant surface 9 on developer roll 8 (if no developer roll sleeve is provided) or, if provided, on developer roll sleeve 8a.
It is likewise desirable to provide a wear-resistant conductive composition to form a coating (having a wear-resistant surface 9) applied either directly onto a developer roll 8 or onto a developer roll sleeve 8a. The wear-resistant conductive composition affixed onto developer roll 8 or onto developer roll sleeve 8a is desirable to improve coating life, to enhance tribo/toner charging, to improve toner release, to prolong charge blade life, to reduce streaking, to reduce ghosting or other undesirable problems associated with repeated use.
Thus, it is desirable to provide a developer roll coated with an improved wear-resistant coating, a method for making the same, a developer roll sleeve coated with the improved coating, and a method for making the same for alleviating one or more of the aforementioned problems.
The following patents may be relevant to various aspects of the present invention: U.S. Pat. Nos. 5,253,019 (Brewington et al.), 5,177,538 (Mammino et al.), 4,505,573 (Brewington et al.), 4,809,034 (Murasaki et al.), 5,300,339 (Hayes et al.), and 5,386,277 (Hays et al.). Each of these patents is incorporated herein by reference in its entirety.